Dyeing of cellulose carboxylic acid esters with vat dyes



" 2,774,649 Patented Dec. 18, 1956 DYEING F CELLULOSE CARBOXYLIC ACID ESTERS WITH VAT DYES No Drawing. Application May 17, 1952,

. Serial No. 288,542

4 Claims. (Cl. 8-36) This invention relates to a process of dyeing esters of cellulose carboxylic acids. Cellulose carboxylic acid esters, such as cellulose acetate, cellulose butyrate, etc., and copolymers have achieved extensive use both in the form of plastics and particularly in. the form of fibers.

A great deal of work has been done on the dyeing of cellulose esters such as cellulose acetate. Very satisfactory dyeing procedures have been developed with dyes which have aflinity for the fibers. In general, the dyeing procedure has been from baths in which the dyestufi is dispersed, particularly baths in which the dispersion is effected by means of soaps. While a wide range of colors has been available by this method, it has not been profitable in the past to dye with vat dyestuffs because the ordinary procedures of vat dyeings either destroy the cellulose ester or do not result in a satisfactory level dyeing. As a result, it has been impossible to use the vat dyes with their advantages from the standpoint of fastness to light and other agents.

According to the present invention, we have found that it is possible to dye cellulose esters with vat dyes in a very narrow pH range of 6 to 8. In this pH range the reduced vat dye is in the presence of its free hydroxyl form, sometimes referred to as a vat acid, although this is a rather loose language as the compounds are not typical acids and are so-called only because they are capable of forming salts with very strong bases as do many other phenols. The present invention is all the more surprising because under the conditions there is no dyeing of cellulose or regenerated cellulose fibers, such as cotton and viscose rayons, for which ordinary vat dyeing procedures are particularly designed. The sodium salts of the leuco vat dyes which are necessary to the dyeing of cellulose compounds will not dye satisfactorily the cellulose esters and correspondingly neither will the free leucos or vat acids dye cellulose fibers under the conditions of the present invention. It is not known why in the narrow pH range of the present invention the dyes show aflinity for cellulose esters of carboxylic acids and it is not intended to base the present invention on any theory of the dyeing mechanism.

It is an advantage of the present invention that any ordinary leuco vat dyestuff can be used and that good dyeings showing excellent penetration levelness and satisfactory fastness may be obtained. In general, it is desirable to dye at high temperatures, preferably above 160 F., and for best and most rapid results, dyeing temperatures at or above the boiling point of water are preferred.

While the present invention depends only on the pH range for its satisfactory operation, and any agent, even dilute caustic alkali, can be used to maintain the pH, the use of such alkali is quite critical, because during the reduction of the vat dyestuff there is a change in pH, due to formation of sodium bisulfate by the oxidation of the reducing agent, sodium hydrosulfite. As a result, rather careful pH control becomes necessary and so in a preferred embodiment of the present invention buffers are used, the best bufiers being polyphosphates such as sodium tripolyphosphate and sodium tetraphosphate. In a more specific aspect of the invention, therefore, these preferred buifers are included as they permit an automatic pH control and make the necessity of careful control during dyeing unnecessary with resulting improved ease of practical operation. Apparently, the polyphosphate buffers act only as pH controls because the same good results are obtainable at the same pH ranges if other means are employed to maintain the range.

While good results are obtainable throughout the range of pHs from 6 to 8, it is preferable to operate between approximately 6.5 and 7.5, and this can be readily assured by the use of sodium tripolyphosphate which is therefore the preferred buffer.

The process of the present invention may be used with either filament or staple yarn and thus opens up a new class of dyes for the dyeing of cellulose ester fibers and materials.

As has been pointed out above, high temperatures are desirable and of course there is an upper limit. This, however, is not determined by the efficiency of the process itself, but rather by the top temperature which the fibers will withstand. In general, temperatures should not go beyond 325 F.

The invention will be described in greater detail in conjunction with the following examples, in which the parts are by weight unless otherwise specified. When parts are specified by volume in the following examples conventional scientific nomenclature is used; in other words, as is conventional in scientific publications when parts by weight and parts by volume are specified they are the parts in the corresponding system, that is to say, when the parts by weight are grams, the parts by volume are cubic centimeters; when the parts by weight are kilograms, the parts by volume are liters, etc.

Example 1 Four parts of a commercial paste of Vat Violet 6R (Color Index No. 1212) was mixed with 30 parts by volume of a 10% solution of sodium tripolyphosphate and 2 parts of sodium hydrosulfite. The mixture was brought to the boil and then made up to a total volume of 200 parts with water at room temperature. Five parts of a skein of cellulose acetate filament yarn was put into the bath and dyed at the boil. After dyeing is complete, the yarn was removed from the bath, washed in warm water and then boiled for five minutes in a 5% soda ash solution. Thereafter the material was again washed in warm water and finished with a solution of 2.5 grams per liter of sodium dodecyl sulfate, the washing being at boiling temperature.

A good level dyeing was obtained which showed satisfactory fastness to light and washing.

Example 2 The procedure of Example 1 was followed but instead of using cellulose acetate filament yarn, cellulose acetate staple yarn was used. The dyeing proceeded in the same manner giving an excellent level shade.

Example 3 The procedure of Example 2 was followed but the vat dye was replaced by 5% of the weight of the yarn of a blue vat dyestuff having Color Index No. 1184. An excellent blue dyeing was obtained which was level and which showed good fastness to light and washing.

Example 4 The procedure of Example 1 was followed using, however, the same blue dyestutf Color Index No. 1184 instead of the vat dye. The temperature during dyeing and the 3 other operations was maintained at a somewhat lower point of 180 F.

Example 5 The procedure of Example 1 was followed using a cellulose acetate butyrate filament instead of cellulose acetate. The dye was Hy-dron Pink (6,6'-dichloro-4,4' dimethyl-2,2-bis thionaphthene indigo) and a good penetration and level dyeing resulted.

Example 6 The procedure of Example 5 was followed substituting the blue vat dyestuft Color Index No. 1184 for the Hydron Pink. A good blue dyeing was obtained.

Example 7 The procedure of Example 1 was followed but instead of employing sodium tripolyphosphate a corresponding amount of sodium tetraphosphate was used. The results were substantially identical with that of Example 1. The tetraphosphate buffered satisfactorily.

Example 8 The procedure of Example 1 was followed but instead of using sodium tripolyphosphate in order to maintain the pH range, 1 part by volume of 30 B. aqueous sodium hydroxide solution was used to maintain the pH. The results were identical with Example 1, but care was required in measuring out the strong alkali,

Example 9 We claim:

1. A method of dyeing cellulose esters of carboxylic acids with vat dyes which comprises heating the said cellulose ester material in an aqueous dyebath containing an unesterified leuco vat dyestufi, a reducing agent and sodium tripolyphosphate and having a pH between 6.5 and 7.5, at a temperature between F. and the boiling point thereof, maintaining the pH of the said dyebath between 6.5 and 7.5 by means of said sodium tripolyphosphate buffer during said heating until the dyeing is complete, and regenerating the vat dye on the said cellulose material by oxidation.

2. The method of claim 1 wherein the said heating and dyeing is efiected at the boil.

3. The method of claim 1 wherein the cellulose ester material is cellulose acetate.

4. A method of dyeing cellulose acetate fibers with vat dyes which comprises heating said fibers in an aqueous dyebath containing an unesterified leuco vat dyestulf, a reducing agent and sodium tripolyphosphate and having a pH between 6.5 and 7.5, at a temperature between 160 and F., maintaining the pH of the said dyebath between 6.5 and 7.5 by means of said sodium tripolyphosphate buifer during said heating until the dyeing is complete, and regenerating the vat dye on the cellulose acetate fibers by oxidation.

References Cited in the file of this patent UNITED STATES PATENTS 1,900,168 Dreyfus Mar. 7, 1933 1,900,172 Ellis Mar. 7, 1933 2,524,073 Olpin Oct. 3, 1950 2,646,339 Ward July 21, 1953 OTHER REFERENCES Chem. Tech. of Dyeing and Printing by L. Diserens, published New York City, 1948, by Reinhold Publishing Corporation, pages 135 and 136. 

1. A METHOD OF DYEING CELLULOSE ESTERS OF CARBOXYLIC ACIDS WITH VAT DYES WHICH COMPRISES HEATING SAID CELLULOSE ESTER MATERIAL IN AN AQUEOUS DYEBATH CONTAINING AN UNESTERIFIED LEUCO VAT DYESTUFF, A REDUCING AGENT AND SODIUM TRIPOLYPHOSPHATE AND HAVING A PH BETWEEN 6.5 AND 7.5, AT A TEMPERATURE BETWEEN 160* F. AND A BOILING POINT THEREOF, MAINTAINING THE PH OF THE SAID DYEBATH BETWEEN 6.5 AND 7.5 BY MEANS OF SAID SODIUM TRIPOLPHOSPHATE BUFFER DURING SAID HEATING UNTIL THE DYEING IS COMPLETE, AND REGENERATING THE VAT DYE ON THE SAID CELLULOSE MATERIAL BY OXIDATION. 